1. Field of the Invention
The present invention relates to a microactuator, and in particular, to an actuator for precisely positioning a magnetic head. Further, the present invention relates to a head gimbal assembly using the actuator and its manufacturing method, and to a hard disk drive using the actuator.
2. Related Art
A hard disk drive, which is a data storage, is provided with a head gimbal assembly on which a magnetic head slider for reading or writing data from/into a magnetic disk, or a storage medium, is mounted. FIG. 7 shows a conventional example of a head gimbal assembly 100.
The head gimbal assembly 100 includes: a magnetic head slider 101; a flexure 102 having a spring property on which the magnetic head slider 101 is mounted on the tip part thereof; an FPC 103 (flexible printed circuit) formed on the flexure 102, for transmitting signals to the magnetic head slider 101; and a load beam 104 supporting the flexure 102. The load beam 104 is mounted on a head arm via a base plate not shown. Further, a plurality of head gimbal assemblies 100 are stacked and fixed to a carriage via respective head arms and pivotally supported so as to be driven rotationally by a voice coil motor to thereby constitute a head stack assembly (not shown).
The head gimbal assembly 100 is driven rotationally by the voice coil motor to thereby position the magnetic head slider mounted on the tip part thereof. In recent years, however, due to an increase in recording density of a magnetic disk, positioning accuracy of a magnetic disk with a control by a voice coil motor is not sufficient.
In view of the above, techniques for more precise positioning have been considered. An example thereof is disclosed in the publication of Japanese Patent Application Laid-Open No. 2002-74870 (Patent Document 1). The configuration of a conventional magnetic head actuator mounted on the head gimbal assembly 100 will be explained below with reference to FIGS. 7 to 11.
As shown in FIG. 7, a magnetic head actuator 110 is mounted on a tongue plane of the flexure 102. The magnetic head actuator 110 is formed in an almost U-shape, and holds the magnetic head slider 101 such that the read/write element is positioned on the opening end side. This will be explained in more detail below.
FIG. 8 shows the configuration of the actuator 110 for precisely positioning the magnetic head, on which the magnetic head slider 101 is mounted. FIG. 5A is a top view, and FIG. 5B is a side view. The magnetic head actuator 110 is formed in an almost U-shape, including a base 111 to be mounted on the flexure 102 and a pair of arms 112 and 113 joined so as to extend in the same direction from the both edges of the base 11, and a space is formed between the pair of arms 112 and 113. In the space between the pair of arms 112 and 113, the magnetic head slider 101 is accommodated and held by the pair of arms 112 and 113. The holding method in this case is, as shown in FIG. 8A, to provide an adhesive 114 such as epoxy resin on the inner sides of the respective arms 112 and 113 at parts near to the tips thereof to thereby fix the side faces near to the tip of the magnetic head slider 101 with the adhesive 114. Since the magnetic head slider 101 is accommodated in the space between the arms 112 and 113 such that the end face of the magnetic head slider 101 of the read/write element side are positioned near the tip parts of the arms 112 and 113, the length of the arms 112 and 113 is formed longer than that of the magnetic head slider 101 in the longitudinal direction.
In FIG. 8B, a magnetic disk will be positioned above the magnetic head slider 101 so as to face the upper surface of the magnetic head slider, so a read/write element (not shown) is formed on the surface facing the magnetic disk (upper surface in FIG. 8B) near the tip of the magnetic head slider 101, and terminals of a read/write element side are formed on the end face of the tip side thereof (left end face in FIG. 8B) (not shown).
Further, the base 111 and the pair of arms 112 and 113 of the magnetic head actuator 110 are integrally formed of a ceramic sintered body having elasticity. However, the joints of the respective arms 112 and 113 to the base 111 (attached parts of the arms) are provided with prescribed notches (gaps), which are filled with elastic bodies 115 such as epoxy resin.
On the side faces positioned outside the respective arms 112 and 113, piezoelectric devices 112a and 113b are mounted (not shown in FIG. 8B), respectively. The piezoelectric devices 112a and 113b expand or contract when a voltage is applied. Thereby, the elastic arms 112 and 113 are deformed in a bending manner almost along the magnetic disk surface. Accordingly, it is possible to swing-drive the read/write element of the magnetic head slider 101 mounted on the tip part of the pair of arms 112 and 113 almost along the magnetic disk surface, whereby precise positioning control can be performed.
Next, a state where the magnetic head actuator 110 is mounted on the flexure 102 in a conventional example will be explained in detail with reference to FIGS. 9 to 11. FIGS. 9 and 10 show the configuration only including the flexure 102 and the actuator 110, in which FIG. 9 is a top view and FIG. 10 is a side view. FIG. 11 shows an FPC 103 as well.
As shown in FIG. 9, the flexure 102 consists of a flexure body 102a forming the tongue plane 102aa of the gimbal structure and a separated part 102b forming flexure side terminals to be connected with head side terminals of the magnetic head slider 101. They are configured to be linked integrally by the FPC 103 as shown in FIG. 11.
First, the notches formed in the attached parts of the respective arms 112 and 113 of the actuator 110 are filled with the elastic epoxy resin 115. Next, the base 111 of the actuator 110 is fixed to a position near to the back end of the tongue plane of the flexure 102, and the tip sides of the arms 112 and 113 are fixed to the separated part 102b with an adhesive 117 or the like. Then, piezoelectric device side terminals, not shown, formed on the side faces of the arms 112 and 113 and trace side terminals formed on the tongue plane of the flexure 102 are connected by metal bonding or the like. Thereby, a voltage which is an expansion/contraction signal is applied to the piezoelectric devices 112a and 113a of the actuator 110 via the FPC 103 and 103b, as shown in FIG. 11.
Next, as shown in FIG. 11, the magnetic head slider 101 is disposed between the pair of arms 112 and 113, and the terminals of the read/write element side of the magnetic head slider 101 and the trace side terminals 103aa of the separated part 102b are connected by soldering 116. Further, the magnetic head slider 101 and the respective arms 112 and 113, that is, the side faces near to the tip of the magnetic head slider 101 and the inner side faces near to the tips of the arms 112 and 113 are fixed to each other with the adhesive 114. Thereby, the read/write element which is the tip part of the magnetic head slider 101 is swing-driven as shown by the arrow X in FIG. 11 together with the separated part 102b linked to the flexure body 102a only with the FPC 103, along with extension or contraction of the arms 112 and 113. This enables precise positioning control with high accuracy.
[Patent Document 1] JP2002-74870A
On the other hand, as the capacity of a hard disk drive increases, the recording density of a magnetic disk further increases. In order to cope with it, although a magnetic head slider of a size called pico slider (e.g., length=1.25, width=1.00, height=0.30) has been used in the conventional example described above, a smaller magnetic head slider of a size called femto slider (e.g., length=0.85, width=0.70, height=0.23) is desired to be used. However, a femto slider is too minute in size of the slider itself, so the strength is weak. Corresponding to it, the actuator described above becomes minute as well, so the strength thereof becomes weak same as the slider. This causes a problem that the reliability might be lowered.
In order to cope with a magnetic disk of high recording density while maintaining the strength, a use of a magnetic head slider formed in a size between the pico slider and the femto slider (hereinafter called as a “pemto” slider) has been considered.
In the case of mounting a pico slider of the conventional example on the actuator 110, on the side of the surface opposite to the flexure 102, the arms 112 and 113 of the actuator 110 and the magnetic head slider 101 are located on the almost same plane as shown in FIG. 10. Accordingly, the flexure body 102a and the separated part 102b are positioned almost on the same plane, so terminals of the separated part 102b and the magnetic head slider 101 can be connected easily.
However, when attempting to realize the technique of connecting the flexure 102 and the magnetic head slider 101 of the conventional example with a pemto slider which is a magnetic slider of a new size thinner than the pico slider, a problem described below may be caused. FIG. 12 shows a state where a pemto slider 101′ is mounted.
The pemto slider 101′ has higher strength since it is not so minute as a femto slider, but is thinner than a pico slider. Therefore, when the pemto slider 101′ is mounted between the arms 112 and 113 as shown in FIGS. 12A and 12B, the distance D between the pemto slider 101′ and the separated part 102b of the flexure 102 becomes longer, which causes a problem that connection between the terminals on the read/write element side formed on the pemto slider 101′ and the trace side terminals formed on the separated part 102b becomes difficult. This is because the upper surface of the pemto slider 101′ in FIG. 12B faces a magnetic disk, so it is impossible to dispose the pemto slider 101′ closer to the flexure 102.
On the other hand, in order to cope with the problem mentioned above, the height of the arms 112 and 113 may be designed to be lower such that the flexure-facing surface of the thin pemto slider 101′ is located on the same plane of the surfaces facing the flexure of the arms 112 and 113. However, this causes a problem that the strength of the important actuator 110, which holds the magnetic head slider 101′ and performs precise positioning control, is reduced same as the case of using a femto slider mentioned above, resulting in lowering of the reliability of the hard disk drive.